The present invention relates to a method of processing of a semiconductor substrate and removing process residue deposited on internal surfaces of a process chamber during processing of the substrate.
In integrated circuit fabrication, semiconductor, dielectric, and conductor materials, such as for example, silicon dioxide, silicon nitride, polysilicon, metal silicide, and silicon layers are formed on a substrate and etched to form features such as gates, vias, contact holes, or interconnect lines. The layers are typically deposited by chemical vapor deposition (CVD), physical vapor deposition, or thermal oxidation processes. For example, in a typical CVD process, thin layers of conducting, semiconducting or dielectric material are deposited on a heated substrate by reactant gases, such as WF.sub.6, SiH.sub.4, SiH.sub.2 Cl.sub.2, WSi.sub.2, or H.sub.2. In an etching process, a patterned etch resistant layer of photoresist or a hard mask is formed on the deposited layer by conventional photolithographic methods, and the exposed portions of the deposited layer are etched by energized halogen etchant gases, such as Cl.sub.2, HBr, and BCl.sub.3. The etchant gas composition also often includes passivating gases, such as CHF.sub.3, which are used to generate passivating deposits on sidewalls of etched features to provide a more anisotropic etching process.
One problem in semiconductor fabrication processes is how to clean the process residue, byproducts, and other deposits that are formed on the walls and other component surfaces inside the process chamber during processing of a substrate. In typical CVD processes, the composition of the process residues and deposits depend on the composition of feed gas, and the temperature of the surfaces on which the process residue are formed. In etch processes, the composition of the etch process residue depends upon the composition of vaporized species of etchant process gas, the substrate material being etched, and the mask or resist layers on the substrate. For example, when tungsten silicide, polysilicon, or other silicon-containing layers are etched, silicon-containing gaseous species are vaporized or sputtered from the substrate. Etching of metal layers results in vaporization of metal species. In addition, the resist or mask layer on the substrate is also partially sputtered or vaporized by the etchant gas to form gaseous hydrocarbon or oxygen species. The resultant vaporized and/or gaseous species in the process chamber condense to form polymeric byproducts composed of hydrocarbon species; gaseous elements such as fluorine, chlorine, oxygen, or nitrogen; and elemental silicon or metal species depending on the composition of the layer being etched. These polymeric byproducts form thin layers of etchant process residues that are deposited on the walls and components in the process chamber. The composition of the process residue typically varies considerably across the process chamber surface depending upon the composition of the localized gaseous environment, the location of gas inlet and exhaust ports, and the process chamber geometry. The process residue must be periodically removed to prevent contamination of the substrates being processed in the process chamber and to provide more consistent processing results.
The process residues and deposits are especially a problem in semiconductor fabricating processes in which a sacrificial material is used to change the distribution or concentration gradient of gaseous species around the substrate. A non-uniform or variable concentration of reactive gaseous species around the substrate causes different processing rates across the surface of the substrate. One way of achieving a more uniform distribution of reactive species is to provide a member composed of a sacrificial material having a surface disposed around the substrate that when exposed to an energized process gas or plasma reacts to release or scavenge gaseous species to alter the composition of the process gas at a peripheral edge of the substrate. For example, in a fluorine containing plasma it is known to use a sacrificial collar comprising an oxygen-containing material, such as quartz (a crystalline form of SiO.sub.2), to provide oxygen species to the process gas around the peripheral edge of the substrate and thereby create a more uniform distribution of the reactive process gas species across the substrate. As another example, a sacrificial collar composed of silicon can be used to scavenge fluorine from the plasma by reacting with gaseous fluorine species to form SiF.sub.6, a volatile compound that is exhausted from the process chamber. However, during the fabrication process, process residues accumulate on the collar forming an impermeable residue layer that blocks or interferes with the exchange of gaseous species between the collar and plasma.
To provide consistent processing from one substrate to another, the reactive surfaces of sacrificial members must be cleaned often to remove the process residue formed on it, thereby allowing it to react with the energized process gas to change the concentration of gaseous species at the substrate edge. One conventional method of removing the process residue is a "wet-cleaning" process in which the process chamber is opened to the atmosphere and an operator scrubs off accumulated process residue with an acid or solvent. To provide consistent process chamber characteristics, after the wet-cleaning process, the process chamber is "seasoned" by pumping down the process chamber for an extended period of time, typically 2 to 3 hours. Thereafter, the process to be performed in the process chamber is performed for 10 to 15 minutes on a series of dummy wafers until the process chamber provides consistent and reproducible results. In the competitive semiconductor industry, the increased cost per substrate that results from the extended process chamber downtime during the wet-cleaning and seasoning process steps, is highly undesirable. Also, the wet-cleaning and seasoning process often provide inconsistent and variable properties. In particular, because the wet-cleaning process is manually performed by an operator, it often varies from one session to another, resulting in variations in process chamber surface properties and low process reproducibility. Thus it is desirable to have a cleaning process that can quickly and reliably remove the process residue formed on the surfaces of the collar.
In one in-situ cleaning method, a cleaning plasma of a reactive cleaning gas, such as an NF.sub.3, is formed in the process chamber to clean all the process chamber surfaces including the surfaces of the sacrificial collar. The cleaning process is typically performed after a certain number of substrates are processed in the process chamber to remove all the process residues formed during the processing of the substrates. The cleaning plasma reacts with the process residue to form volatile compounds which are exhausted from the process chamber. However, unlike the wet-clean process in which the operator can selectively clean only the sacrificial collar, the in-situ cleaning plasma cleans all the surfaces in the process chamber. Because of the large area of the exposed surfaces in the process chamber, this cleaning process can take over 15 hours, and the long cleaning time significantly reduces the number of substrates which can be processed in a given time period and increases capitalization costs. In addition, in-situ cleaning plasmas tend to preferentially remove only some of the process residue. In particular, only soft components of the process residue are removed, leaving hard components that later flake-off and contaminate the substrate. It is desirable to have a cleaning process for efficiently removing the process residues deposited on process chamber components.
Another problem with in-situ cleaning processes arises because the cleaning plasma is operated at relatively high power level to achieve an acceptable cleaning rate for cleaning all the process residues in the process chamber. The high power plasma erodes internal process chamber surfaces, such as aluminum surfaces, and damages process chamber components, such as erodible polymer layers, for example, polyimide electrostatic chucks. In addition, the cleaning plasmas often only partially clean the anodized aluminum liners that line the walls of the process chamber that serve as a surface for preferential deposition of process residue. Typically, the process chamber liners are maintained at a low temperature to act as a "sink" for the deposition of volatile process residues. The large amount of process residue that deposits on the liner surfaces is difficult to completely clean off, and partially cleaned residue will flake-off and contaminate the substrate. Moreover, the high power plasma also tends to generate other residue byproducts that cannot be removed except by physically wiping the internal surfaces of the process chamber. For example, NF.sub.3 plasma used to clean aluminum process chamber surfaces can form a layer of Al.sub.x F.sub.y compound on the aluminum process chamber surfaces that cannot be easily removed.
Thus it is desirable to have a cleaning plasma that can be used to selectively clean only a portion of the process chamber. To avoid residue flaking, it is also desirable for the cleaning process to remove substantially all the process residues deposited on selected process chamber surfaces without reaching, and incompletely cleaning, other surfaces in the process chamber. There is also a need for a method of removing process residues and deposits without damaging or eroding process chamber components. There is a further need for a method of efficiently removing process residues without forming other unwanted deposits on the process chamber surfaces.